Mercury is often present in natural gas, petrochemical and some refinery feed steams. Petroleum reservoirs in some regions of world (e.g., North Sea, Asia) contain elevated concentrations of mercury. Further, many deeper, hotter reservoir zones that contain elevated mercury concentrations are being produced as shallower, cooler zones are depleted.
This mercury contamination is becoming a significant problem for upstream and downstream operations in the petroleum industry. The petroleum-wetted surfaces of equipment (e.g., pipes, valves, vessels) and processing materials (e.g., catalyst particles, separator solids) in refineries and gas plants that process mercury-containing feed stocks become contaminated with such mercury compounds. These contaminated surfaces must be cleaned periodically to remove the mercury compounds from the equipment and processing materials.
Traditionally, steam cleaning has been used to clean water-soluble forms of mercury. However, steam cleaning fails to remove insoluble forms of mercury (e.g., HgS). Further, the elevated temperature of steam vaporizes elemental mercury into the air, which creates a significant health hazard for any employees in the vicinity of the cleaning operation.
Other cleaning procedures utilize water-based mixtures of oxidizing agents and complexing agents to solubilize the mercury. These corrosive solutions cannot be used on most plant equipment (e.g., pipes, valves, vessels) without seriously damaging the metal surfaces.
Accordingly, a safe, noncorrosive cleaning process is needed to remove mercury contamination from solid surfaces and hydrocarbon oils.